Does the math.
True. Then again, that's plausibly not known. In fact it now occurs to me that for "from 20,000 to 5,000 years ago the daelkyr ruled Xen'drik" (made up Eberron-inspired line) one could say that's too much information, rather than too little. Compared to "daelkyr ruins exist, usually below giant ruins." without a pretense of even approximate dating.if the dungeons are tombs it would be helpful to know exactly whose